Metal amino acid or protein hydrolysate chelates have been referred to in the art as being water insoluble metal proteinates containing at least two ligands per metal ion present. They are described as such in U.S. Pat. Nos. 4,020,158; 3,969,540; 3,775,132, and 3,396,104.
The proteinate is formed by complexing a protein hydrolysate having protons removed therefrom by pH adjustment until the hydrolysate molecule is electronegative. The electron rich hydrolysate is then reacted with a bivalent metal ion to form a "claw-like" structure known as a chelate.
The chelate is formed by first dissolving a water soluble metal salt in water. The metal ion will have a valence of plus two or more but that does not define all of the reaction sites of the ion. The ion will contain a certain but varying number of waters of hydration known as coordination complexes that may be represented by the following formula using a zinc ion and four waters of hydration. ##STR1##
Using glycine as the simplist protein hydrolysate it will exist as a zwitter ion at its isoelectric point and have the formula: ##STR2##
Upon raising the pH, the protons are removed leaving an electronegative hydrolysate or the formula: ##STR3##
By combining the electronegative protein hydrolysate with a metal ion the following reaction is thought to initially occur: ##STR4##
Upon the addition of more base (NaOH) the product becomes a chelate having the formula ##STR5##
It will be noted that the zinc is completely protected from ionization. Metal proteinates have relatively high stability constants on the order of 10.sup.7-12. The citrates and ascorbates form much weaker chelate bonds on the order of 10.sup.2-4 and EDTA (ethylenediaminetetraacetic acid) and its derivatives form a strong chelate having a stability constant on the order of 10.sup.16-28. The citrates and ascorbates tend to decompose before they can be assimilated into a biological system and it is much more difficult to absorb a positive metal ion than a chelate. EDTA and its derivatives form such strong chelate bonds that they pass intact through most biological systems whether they be plants or animals, including humans. For this reason EDTA is often administered as a metal scavenger to remove unwanted metal ions from biological systems. Metal proteinates are sufficiently stable that they are abosrbed into biological systems whether they be plants or animals, including humans. For this reason EDTA is often administered as a metal scavenger to remove unwanted metal ions from biological systems. Metal proteinates are sufficiently stable that they are absorbed into biological systems where the chelate bonding is broken and the metal ion and amino acid are utilized by the biological system at the appropriate place. In an animal for example, most metal absorption occurs in the small intestine. The metal proteinate then must be sufficiently stable to pass through the acidic stomach media into the small intestine.
In the past, metal proteinates have been insoluble and have been mixed with food or administered in tablet or capsule form. This may not be convenient when using them for plants and animals including man.